Stent having a multiplicity of undulating longitudinals

ABSTRACT

The present invention provides for an expandable stent (10 or 20) for use in an artery or other vessel of a human body. The stent structure (10 or 20) maintains the patency of the vessel within which the stent (10 or 20) is expanded radially outward. One embodiment of the present invention is a stent (10) having a multiplicity of frames (12) joined together by at least two undulating longitudinal structures (14L and 14R) which can readily change their length in the longitudinal direction so as to provide increased longitudinal flexibility for the stent (10) for easy passage through and placement within a curved vessel such as a coronary artery. The stent (20) is an embodiment of the present invention having frames (22) joined with longitudinal structures (24B, 24T and 24R) and formed from a single, thin-walled piece of metal by means of laser cutting or chemical etching. Because the stent (20) is fabricated from a single piece of metal, it provides a multiplicity of closed perimeter cells that are formed as a continuous metal structure.

This is a continuation of application Ser. No. 08/202,128 filed on Feb.25, 1994 now U.S. Pat. No. 5,643,312.

FIELD OF THE INVENTION

This invention is in the field of stents for maintaining patency of anyone of a multiplicity of vessels of the human body.

BACKGROUND OF THE INVENTION

In the last decade, many different designs of stents have been used tomaintain patency of arteries and other vessels of the human body. In allsuch devices, hoop strength is an important characteristic.Specifically, the stent must have enough hoop strength to resist theelastic recoil exerted by the vessel into which the stent is placed. TheMass stent described in the U.S. Pat. No. 4,553,545 and the Dotter stentdescribed in U.S. Pat. No. 4,503,569 are each open helical coils. ThePalmaz stent described in the U.S. Pat. No. 4,733,665 is of the "chinesefinger" design. The Gianturco-Rubin stent currently sold by Cook, Inc.is another stent design which like the stents of Mass, Dotter and Palmazdoes not have any closed circular member to optimize hoop strength.

The ideal arterial stent utilizes a minimum wire size of the stentelements to minimize thrombosis at the stent site after implantation.The ideal arterial stent also posses sufficient hoop strength to resistelastic recoil of the artery. Although the optimum design for maximizinghoop strength is a closed circular structure, no prior art stent hasbeen described which has a small diameter when percutaneously insertedinto a vessel and which expands into the form of multiplicity of closedcircular structures (i.e. rings) expanded outward against the vesselwall.

BRIEF SUMMARY OF THE PRESENT INVENTION

The present invention is an expandable stent that can be used in anartery or any other vessel of the human body which, when expanded, formsa mutiplicity of generally circular rings whose closed structureoptimizes hoop strength so as to minimize elastic recoil of the vesselinto which the stent is inserted. Furthermore, the structure of thestent in the present invention is initially in the form of foldedellipses or ovals which can be formed to a small diameter forpercutaneous insertion by means of a stent delivery catheter. The ovalsare joined to each other by either a straight or undulating shaped wireswhich are called "longitudinals" which serve to space the deployed ringswithin the vessel. Straight longitudinals are used in straight vesselsand undulating longitudinals can be employed in either straight orhighly curved vessels such as some coronary arteries.

Thus, an object of this invention is to provide a stent having a maximumhoop strength by the employment of closed, generally circular structureswhich are in fact rings.

Another object of this invention is that the rings are initially in theform of ovals that can be folded to fit onto a cylindrical structure ata distal portion of a stent delivery catheter.

Still another object of this invention is that the fully deployed ringsare spaced apart by means of longitudinals which are either straight ofundulating wires that are placed to be generally parallel to thelongitudinal axis of the vessel into which the stent is deployed.

Still another object of this invention is that the pre-deployment stentstructure is formed as a single piece out of a metal tube having asmaller inside diameter as compared to the outside diameter of anexpandable balloon onto which the pre-deployment stent is mounted.

These and other important objects and advantages of this invention willbecome apparent from the detailed description of the invention and theassociated drawings provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the stent after it has been deployed; i.e., inits post-deployment form.

FIG. 2 is a transverse cross section at section 2--2 of FIG. 1illustrating how the longitudinals are joined to the rings.

FIG. 3 is a cross section at section 3--3 of FIG. 2 showing the joiningof a single ring to the longitudinals.

FIG. 4 is a side view of the stent prior to being mounted onto a stentdelivery catheter; i.e., in the form of an initial structure.

FIG. 5 is a transverse cross section at section 5--5 of FIG. 4illustrating how the longitudinals are joined to the ovals.

FIG. 6 is a side view of a pre-deployment form of the stent structure inwhich the ovals have been folded into a small diameter cylinder that isplaced around a deflated balloon situated near the distal end of a stentdelivery catheter.

FIG. 7 is a partial side view of a pre-deployment stent structureshowing only two of a multiplicity of folded ovals formed around anexpandable balloon in which the ovals are folded in an alternativemanner as compared with FIG. 6.

FIG. 8 is a side view of a post-deployment stent structure whichutilizes two undulating longitudinals on opposite sides of the stent forimproved placement in curved vessels.

FIG. 9 is a side view of a stent as etched out of a small diameter metalcylinder as a single piece of metal.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the cylindrical stent 1 of the presentinvention shown in its post-deployment configuration. The stent 1 has amultiplicity of rings 2 which are spaced apart by four wires calledlongitudinals. As seen in FIGS. 1 and 2, at the top of the stent islongitudinal 4T, at the bottom is longitudinal 4B, at the left side islongitudinal 4L and at the right side is longitudinal 4R. Although FIGS.1 and 2 show 7 rings and 4 longitudinals, it is apparent that the stentcan be made longer by adding rings or increasing the separation betweenrings. In a similar manner, the stent can be made shorter by reducingthe number of rings or decreasing the spacing between rings. Alsovariable spacing of the rings is envisioned for accomplishing a varietyof purposes including increased hoop strength at a particular section ofthe stent. Also, it is envisioned that the two or more longitudinalscould be utilized for this stent design with a maximum number being 32.

FIGS. 2 and 3 illustrate the joining of the longitudinals to the rings.Specifically the longitudinals can be placed into cutouts in the form ofnotches 5 located on the outside perimeter of the ring 2. Thelongitudinals can then be spot welded, adhesively bonded or joined byany variety of means to the rings 2. It is also envisioned that thelongitudinals could be placed on the inside perimeter of the ring 2, orholes could be mechanically or laser drilled through the ring 2 forplacement therethrough of the longitudinals.

FIGS. 4 and 5 illustrate a stent 1' shown in one particular form inwhich it could be fabricated; i.e., in an initial structure form.Specifically, FIGS. 4 and 5 show that this initial form of the stent 1'is a multiplicity of parallel ellipses or ovals 2' each oval having thesame minor axis dimension m and major axis dimension M. The oval's minoraxis passes through the center of the longitudinals 4L and 4R. Theoval's major axis passes through the center of the longitudinals 4T and4B. It is important to note that, if it is desired to have a finaloutside diameter D (as seen in FIG. 2) of the ring 2 after it is fullydeployed, then it can be shown that D is given by the equation D²=1/2(m² +M²).

To place the stent design of FIGS. 4 and 5 onto a balloon that ismounted near the distal end of a stent delivery catheter, it isnecessary to fold the ovals 2' around that balloon. Specifically, thepre-deployment cylindrical stent 1" can be formed onto an expandableballoon 6 as shown in FIG. 6 by folding the ovals 2' about the dottedline F (which is the minor axis of the oval 2') as shown in FIG. 5.Specifically, as seen in FIG. 4, the top and bottom of the ovals 2'could be held stationery while the side longitudinals 4R and 4L arepushed to the left which results in the pre-deployment structure whichis shown as the stent 1" in FIG. 6. An optimum design has the foldedovals 2" as shown in FIG. 6 with the stent 1" being a cylinder whoseoutside diameter is equal in size to the minor axis dimension m. Whenthe balloon 6 of FIG. 6 is expanded, the pre-deployment stent 1"structure forms the post-deployment stent 1 structure having circularrings 2 as shown in FIGS. 1 and 2.

The stent 1'" is an alternative embodiment for a pre-deploymentstructure of the stent of the present invention as it is placed onto aballoon. Specifically, FIG. 7 shows 2 folded rings 2'" of a multiplering stent 1'". The stent 1'" being formed by holding the top and bottomof the stent 1' of FIG. 4 stationery while pushing the longitudinal 4Rto the left and pushing the longitudinal 4L to the right. Like the stent1" of FIG. 6, when mounted onto a balloon, the stent 11'" has acylindrical shape with a diameter equal to the dimension m.

FIGS. 1 to 7 inclusive illustrate stents that employ longitudinals thatare formed from generally straight wires. FIG. 8 shows an alternativeembodiment of a stent 10 that has two undulating longitudinals.Specifically, the left side longitudinal 14L (shown as dotted lines) andthe right side longitudinal 14R are each undulating shapedlongitudinals. A stent such as stent 10 could have two or moreundulating longitudinals. Such a stent would bend more easily duringinsertion into a vessel and would be more readily adaptable forplacement in curved vessels such as some coronary arteries.

Typically, the rings and longitudinals of the stents would be made ofthe same material. Typical metals used for such a stent would bestainless steel, tantulum, titanium, or a shape memory metal such asNitinol. If Nitinol is used, the stent would be heat treated into theshape at body temperature having circular rings 2 as shown in FIGS. 1and 2. The rings could then be distorted into ovals as shown in FIGS. 4and 5 and then mounted onto a stent delivery catheter which does notemploy a balloon but is of the more general shape described in thepreviously cited U.S. Pat. No. 4,553,545 by C.T. Dotter. Such a designwould provide the desired stent structure having a multiplicity ofgenerally circular rings instead of the Dotter design of a helicalspring which inherently has a lesser hoop strength as compared to thepresent invention.

It should be understood that once the ovals are folded onto a stentdelivery catheter, when they fully deploy, they do not form perfectlycircular rings as shown in FIG. 2, but rather they are of a generallycircular shape. Such comparatively small deviations from an exactlycircular shape do not appreciably decrease hoop strength because theyare in fact closed structures that are almost exactly circular.

It should also be understood that at least part of the end rings of thestent could be fabricated from or coated with a radiopaque metal such astantalum or gold to provide a fluoroscopic indication of the stentposition within a vessel. However, the other rings and the longitudinalscould be made from a much less dense metal which would provide lessobscuration of the central region within the stent. For example, thestent rings and longitudinals could all be fabricated from titanium or atitanium alloy except the end rings which could be formed from goldwhich is then plated with titanium. Thus, the entire outside surface ofthe stent would be titanium, which is known to be a comparativelynon-thrombogenic metal while the gold in the end rings provides animproved fluoroscopic image of the stent extremities.

The dimensions of stent rings are typically 0.1 to 0.3 mm thick, with awidth of 0.1 to 0.5 mm and an outside diameter D between 2.0 and 30.0 mmdepending on the luminal diameter of the vessel into which it isinserted. The length of the stent could be between 1 and 10 cm. The wirediameter for the longitudinals would typically be between 0.05 and 0.5mm.

Although the designs of FIGS. 1 through 7 inclusive illustrate separatelongitudinals attached to a multiplicity of rings, this invention alsocontemplates an initial stent structure which is chemically etched fromthin-walled tubing having an oval transverse cross section. Thus theoval and longitudinals would be formed from a single piece of metal thusprecluding the need for attaching the longitudinal to the rings. In asimilar manner laser or EDM machining could be used to form the stentfrom a thin-walled tube.

It is further anticipated that a pre-deployment stent structure 20 asshown in FIG. 9 could be formed from a thin-walled cylindrical tubewhose inside diameter is slightly smaller than the outside diameter ofthe balloon 6 shown in FIG. 6. A pattern such as that shown in eitherFIG. 6 or FIG. 7 could be photoetched onto a thin-walled metal cylinder.The one piece structure 20 shown in FIG. 9 has folded ovals 22 andlongitudinals 23T, 24B, 24R and (not shown) 24L. This pre-deploymentstent structure 20 could then be mounted onto the expandable balloon;the stent having sufficient elastic recoil to firmly grasp down onto theballoon.

Various other modifications, adaptations, and alternative designs are ofcourse possible in light of the above teachings. Therefore, it should beunderstood at this time that within the scope of the appended claims,the invention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A stent structure for maintaining patency of avessel of a human body comprising a multiplicity of structures forminglongitudinals extending in a substantially longitudinal direction, atleast a portion of at least one of said longitudinals having anundulating shape.
 2. The stent structure as recited in claim 1 includinga frame extending around a longitudinal axis of said stent structure,said longitudinals being fixedly coupled to said frame.
 3. The stentstructure as recited in claim 2 where said frame is formed of at least apair of longitudinally displaced frame elements, said longitudinalsbeing secured to at least two of said frame elements.
 4. The stentstructure as recited in claim 3 where said frame elements are formed ina closed contour.
 5. The stent structure as recited in claim 3 wheresaid frame includes a pair of opposing end frame elements having aradiopacity value different than a radiopacity value of other frameelements forming said frame.
 6. The stent structure as recited in claim3 where said stent structure is formed from a metal having a shapememory characteristic.
 7. A stent structure for maintaining patency of avessel of a human body comprising:(a) a frame displaceable in a radialdirection for contiguous interface with an inner wall of said vessel ofsaid human body; and, (b) a multiplicity of longitudinals secured tosaid frame, at least two of said longitudinals having an undulatingcontour for enhancing longitudinal flexibility.
 8. The stent structureas recited in claim 7 where said longitudinals extend in a substantiallylongitudinal direction.
 9. The stent structure as recited in claim 7where said frame includes a plurality of longitudinally displaced frameelements, each of said frame elements being fixedly coupled to at leastone of said longitudinals.
 10. The stent structure as recited in claim 8where said frame elements are formed in closed contour formation. 11.The stent structure as recited in claim 8 where said frame elements areformed of wire members.
 12. The stent structure as recited in claim 8where said longitudinals are formed of wire members.
 13. The stentstructure as recited in claim 8 where said frame elements and saidlongitudinals are formed of a metal composition.
 14. The stent structureas recited in claim 9 where said frame includes a pair of longitudinallydisplaced end frame elements having a differing radiopacity when takenwith respect to at least one other frame element of said frame.
 15. Apre-deployment stent structure having a longitudinal axis comprising atleast two longitudinal structures each having at least one straightsection and at least one undulating section with each said straightsection being joined continuously to said at least one undulatingsection, the straight sections of all of the longitudinal structuresbeing generally parallel to the longitudinal axis of the stent, theundulating section of each longitudinal structure extending generally ina circumferential direction and being of a generally curved shape so asto allow each undulating longitudinal structure to readily change lengthduring insertion of the stent structure into a curved vessel of a humanbody.
 16. The pre-deployment stent structure of claim 15 wherein theundulating section of the longitudinal structures extend first in onecircumferential direction and then extend in the oppositecircumferential direction.
 17. The pre-deployment stent structure ofclaim 15 wherein each undulating section is joined at each of its endsto a straight section.
 18. The pre-deployment stent structure of claim15, wherein each undulating structure is in the general form of a sinewave.
 19. The pre-deployment stent structure of claim 15 in which thestent is formed as a one piece structure that is photo-etched from asingle piece of metal.
 20. The pre-deployment stent structure of claim15 in which the stent is formed as a one piece structure that is EDMmachined from a thin-walled tube.
 21. The pre-deployment stent structureof claim 15 in which the stent is formed as a one piece structure thatis laser machined from a thin-walled tube.
 22. A pre-deployment balloonexpandable stent structure adapted for percutaneous delivery to thecurved coronary arteries, the stent structure being generally in theform of a thin-walled metal tube having a longitudinal axis, the stentstructure having a multiplicity of closed perimeter cells, each cellhaving one or more undulating sections, each undulating section having agenerally curved shaped and having a first end point and a second endpoint wherein a line drawn from the first end point to the second endpoint is generally parallel to the stent's longitudinal axis.
 23. Thestent of claim 22 wherein the line drawn from the first end point to thesecond end point of the generally curved shape remains generallyparallel to the longitudinal axis of the stent as the stent is expandedinto its post-deployment state.
 24. The stent of claim 22 wherein eachcell has at least one circumferentially adjacent cell which shares oneundulating section.
 25. The stent of claim 22 wherein the undulatingsection of each closed perimeter cell comprises a "U" shaped curve. 26.A balloon expandable coronary stent comprising:(a) a stent in the formof a thin-walled metal tube capable of being mounted on an expandableballoon for percutaneous delivery of the stent into a coronary artery,the stent having a plurality of zig-zag segments, the zig-zag segmentscapable of being expanded by the balloon; and, (b) a plurality oflongitudinally undulating sections of a generally curved shapepositioned between and connecting the zig-zag segments, wherein theplurality of longitudinally undulating sections can expand and contractin length while being passed through a curved coronary artery.